This invention is directed to a process and apparatus for applying size to glass fibers and, more particularly, to a process for modifying the viscosity of the size once it has been applied to glass fibers and apparatus for carrying out that process.
Glass fibers are useful in a variety of technologies. For example, glass fibers are commonly used as reinforcements in polymer matrices to form glass fiber reinforced plastics or composites.
As is known in the art, glass fibers which are intended for use as reinforcements usually require a size. The size, also commonly referred to as "sizing composition," serves to provide a lubricating quality to the individual fibers to provide them with abrasion resistance.
Glass fibers are susceptible to breakage if scratched or otherwise damaged. Scratches and surface defects sometimes occur as the fibers come into contact with one another during fiber production. The breakage of a single fiber during the manufacture of a plurality of glass fibers (e.g., 5000 fibers) interrupts fiber production. In order to reduce breakage and other related problems, size is applied to the fibers during fiber production. That is, the glass fibers are sized with a protective material substantially immediately after they are formed.
In the process of producing glass fibers, size is applied as the fibers are mechanically drawn from a molten glass source, such as a bushing. If a glass fiber package is being formed, the sized glass fibers are gathered into a strand and wound onto a collet. During winding, a significant amount of sizing composition is lost as a result of centrifugal forces occurring during the winding process. The portion of the size lost during winding is referred to as "slingoff." The loss of materials resulting during winding is dependent upon, among other things, the speed of the winding process. At typical winding speeds, a conventional glass fiber manufacturing line will lose approximately 45 percent of the chemicals applied to the fibers. This represents a significant amount of waste that results in higher production costs.
One attempt made in the past to reduce the amount of slingoff involves increasing the viscosity of the sizing composition before it is applied to the glass fibers. However, the thickened sizing composition results in an increase in fiber breakage at the applicator roller. The thickened sizing composition also makes it difficult to apply a uniform coating of sizing composition to the fibers.
Accordingly, a need still exists for an improved size coating process which reduces size slingoff.